Metallurgical treatment for silver ores.



f in the Grand Duchy of Baden, Germany,

UNITED STATES,

PATENTOFFIOE.

METALLURGICAL TREATMENT OF SILVER ORES.

1,085,675. No Drawing.

To all whom it may concern.

Be it known that I, OSCAR DYCKERHOFF, doctor of philosophy, and acitizen of the German Empire, and resident of Karlsruhe,

with the post-office address VVestendstrasse 52, have invented new anduseful Improvements in the Metallurgical Treatment of Silver Ores, ofwhich the following. is a specification.

The processes for the metallurgical treatment of complex silver ores orsilver residues, which contain the silver wholly or in part in themetallic condition, in no way produce the results which are to beexpected of a process that is even only to some extent satisfactory.

The usual smelting operation yields, as might be expected from thecomposition of the Canadian ores for example, wholly insuflicientresults, even when the smelting is conducted in a vacuum furnace with orwithout a preliminaryv roasting to eliminate arsenic, always a difiicultoperation.

For want of a suitable process it has been necessaryfitd sell the richerportions of the ore to the large lead smelters who have used it as adirectaddition to the shaft furnaces and have paid only for the silver,and even for this only with deductions.

A rational, cheap process, which permits the recovery ofall the silverand at least the larger part of the cobalt, nickel and arsenic, hashitherto been wanting. A simple chloridizing roasting with addition ofcommonsalt, applicable in the case of similar ores poor in silver is acomplete failure when larger proportions of metallic silver are present.It has now been found, however, that it is possible easily to chloridizethe silver even when present in large proportion, if there be added tothe mixture of ore and salt, before it is roasted, clay or ordinaryloam. With this addition there occurs at a suitable temperature adecomposition of the salt in the sense that sodium silicate is formedand chlorin or hydrochloric acid liberated, which attacks the silverenergetically while the alumina and in particular the undecomposed clayused in excess absorbs the silver chlorid and so gives the hydrogenchlorid opportunity to attack and further chloridize metallic silver.when used instead of clay satisfactorily de- Specifieation of Letterslatent.

Quartz powder Patented Feb. 3, 1914.

Application filed February 13, 1913. Serial No. 748,107.

composes the salt but does not act by any means equally well.

The said decomposition of the salt occurs quickly and easily at a brightred heat; at

a dark red heat, however, it is very incomplete and gradual. Now, sincefor the purpose of losing as little silver as possible, it is anessential condition of chloridizing roasting that the temperature shouldbe as/low as 4 possible, a further addition must be made which willinduce\ the aforesaid reactions and carry them to completion at a quitedark red heat. Such an addition is pyrites, or sulfur and metal oxids,or sulfids in general which are capable of being roasted. These do notexclude the necessity for the presence of clay. On the contrary, thesilica of the clay substance now liberated from the latter by thesulfuric acid produced during the roasting acts energetically on thesalt and liberates the hydrochloric acid of chlorin required for thechloridizing roasting essentially more easily than-when there is noaddition of pyrites. The addition of pyrites, however, must be made notonly with re-' spect to the object of decomposing the salt forchloridizing the sulfur, but with respect to the content of cobalt,nickel and lime in the ore. During the roastin of the ore the cobalt andnickel must be rought into a form of combination, such that these metalscan be dissolved completely or, at least in greater part by the diluteacid produced by absorption of the gases from the roasting furnace inthe usual absorption towers. This form is the'basic sulfate as it isobtained by roasting the aforesaid mixture of ore, common salt, pyritesand clay. Since the sulfates of nickel and cobalt begin to decomposeinto oxids at 600 C. it is necessary when thesemetals are to be Won, notto exceed a temperature of about 580 C., that is a dark red heat.

If a cherry red heat of about 750 C.

were used during the roasting, at which temperature the chloridizing ofthe silver would becompleteeven without the aid of pyrites, extractionof the cobalt and" nickel from the roasted ore'by the weak tower acidwould be impossible. On the other hand a temformed during theroastingfrom the common salt, the calcium being transiently present as calciumchlorid in the mass being roasted. The following equations representthese changes:

I. NaC1+2S0 +2H O+2O:

4Ho1+2Na. so,

II. 2CaCO +4HCl= I 2CaOl +2H O+2CO The sodium chlorid being reproduced,the decomposition begins again to continue so long as calcium carbonateand sulfur dioxid (from the pyrites) are. present.

. [The simple final result of the several reactions which occur are asfollows: All the silver, free and combined, is converted into chlorid;cobalt and nickel are in greater part present as basic sulfate; all limeis converted into sulfate. The greater part of the arsenic remains assodium arsenatetogether with sodium sulfate in the roasted mass and isdissolved by the tower acids; another smaller part passes away asarsenious acids I with the furnace acids and is caught in the absorptiontowers. The furnace gases contain hydrochloric and sulfuric acid besidesalittle chlorin; they are recovered in condensing towers of usualconstruction and are then used as tower acid for extracting the cobalt,nickel and arsenic. Since, however, by a single roasting only some 11-12per cent. of silver can be extracted, the roasting must be repeated whenores which contain more than about 10 per cent. of silver are undertreatment, so as to extract by stages an ever decreasing percentage ofsilver, until there is only a quite inconsiderable proportion left inthe residue. We shall call this step by step procedure roasting instages. It is also found that when such large proportions of chlorid ofsilver are formed in the ore a leachin operation must follow eachroasting and, fiirther that it is better to dissolve first the cobalt,nickel and arsenic (the lastas sodium arsenate) :by' means of the toweracid and then to extract the silver chlorid with sodium thiosulfate orammonia; the dried residue from the leaching is mixed with a freshquantity of salt, pyrites and clay and again roasted. From the foregoingresults of my investigations I have developed a metallurgical treatmentof the Canadian ores (for instance the silver ores of Ontario whichcontain cobalt, nickel and arsenic) which I select as typical examplesof the complex ores in question, which treatment may be expressed asfollows: The ore is suitably subdivided. For the sake of procuringsatisfactory mixing the salt, pyrites and clay, which latter may '7 inpart atleast be the dry residue from the leaching operations, are addedbefore the pulverizing or like operation. The succeeding processes areas follows: Roasting of the mixture in mechanical roasters (these may beused. in all the roastings) until no more gases are evolved at a darkred heat. Leaching with tower acid for extraction of cobalt, nickel andarsenic. Leaching-with sodium thiosulfate or calcium thiosulfate orammonia for extracting silver. The washed residue is dried and theroasting and leaching repeated until the small proportion of metal inthe residue from the lefiilching renders further repetition unprofita e.

Instead of pure iron pyrites, poor sulfur ores in which the sulfur hashardly any value for other purposes may be used, and even ores of thiskind which contain amore or less high content of copper. The coppersulfid is in this case roasted-to copper chlorid and extracted by thetower acid. The combined leaching liquors containing the cobalt, nickeland arsenic, in the eventof their containing copper derived from-theores or from the additions which have been made, are mixed in the coldwith calcium sulfid or sodium sulfid, then separated from theprecipitated copper sulfid, then treated with fresh ore containingcalcium carbonate so as to neutralize the free acids present (this oreis afterward added to the mixture to be roasted) and then treated withcalcium sulfid or sodium sulfid to precipitate the cobalt and nickelwhich are worked up in the usual manner. The remaining liquor whichcontains sodium arsenate as well as sodium sulfate is evaporated tocrystallization for the purpose of either recovering the salts as such,or after further treatment with suitable substances. The combined silverliquors obtained from the several stages of the roasting are mixed witha solution of calcium sulfid or sodium sulfid in die proportion. Theprecipitated silver sulfid is worked up into metallic silver in theknown manner and the regenerated liquor is returned to the process. I

* It is to be observed that for the clay used as an addition there maybe substituted wholly or in part loam, or sand containing clay or marl.In the case of ores poor in silver, pure sand may be. used instead of'traction there may be given the results of two experiments, which'I haveperformed .centrated sulfuric acid) and then the silver was extracted bymeans of a solution of sodium thiosulfate of 5 per cent. strength;

Results of the first series of roasting in stagesAmount of silverextracted after the several roastings. I

11% Roasting 11. 34 per cent-67. 54 per cent. of the total silver.

5. 38 per cent.=32. 06 per cent. of the total silver. 0. 052 per cent.=0. 31 per cent. of the total silver.

per cent.==99.91 per cent. leaving in the residue 0. 016 per cent.= 0.09 per cent.

Results of the second series of roasting in stages-Silver, cobalt andnickel extracted after the several roastings.

1%. Roasting +Ni and 12. 64 Ag.=75. 85% of the total silver.

and 3.10% =18.603 of the total silver. III. 2.39% and 0.72% 4.32% of thetctalsllver. IV. 1.10% and 0.156% 0.934% of the total silver.

13.78% and 16.616% =99.7071eavlngin the residue 4.30% and 0.048% 0.29.

In the preceding table the values left in theresidue are calculated onthe Values in the original ore under treatment. In these experiments theresidue contained 1.3 per cent. of arsenic so that about 95 per cent. of

the total arsenic was recovered.

Now what I claim and desire to secure by Letters. Patent is thefollowing: 1. The process for treating silver bearing materialscontaining cobalt, nickel and arsenic, which conslsts in converting thesilver, cobalt, nickel and arsenic into soluble compounds by roastingthe ore at a suitable temperature with addition of an alkali chlorid andan aluminium silicate and then separating the said soluble compoundsfrom the mass by suitable leaching agents, sub

, stantially as described.

- soluble compounds from the mass by 2. The process for treating silverbearing materials containmg cobalt, nickel and arsenic, which consistsin converting the silver,

cobalt, nickel and-arsenic intosoluble com pounds by roasting the ore ata suitable temperature with addition of an alkali said soluble compoundsfrom the mass by,

suitable leaching agents, substantially as described.

4. The process for treating silverbearing materials containin cobalt,nickel and arsenic, which consists in converting the silver, cobalt,nickel and arsenic into soluble compounds by roasting the ore at asuitable temperature with addltion of common salt, leached residueswhich contains clay, and.

pyrites, and then separating the said soluble compounds from the mass bysuitable leaching agents, substantially as described.

In testimony, that I claim the foregoing -as my invention, I have signedmy name in presence of two witnesses, this 3rd day of February, 1913. I

' OSCAR DYCKERHOFF. Witnesses:

EVA SATTLER,

HERMAIINN Wnrn.

